The Use of Autologous 111In-Labelled Platelets and Scintigraphy to Illustrate Enhanced Platelet Activity During Erection in the Chacma Baboon

Accumulation of platelets as a key mechanism of human erection

In this study, the role of platelets in the human erectile response was assessed. Twenty patients with erectile dysfunction were studied by means of (111)In-oxine-platelets and blood pool imaging using 99mTc. Seventeen patients received intracavernously prostaglandin E1, and three patients received papaverine together with phentolamine. In patients who responded with erection, an increase by between 16 to 137% platelets/ml and a rapid platelet accumulation in the penis during the initial phase of erection were observed. In patients without erection, no change in local platelet concentration occurred. It is likely that platelets play a major role in human erection, probably by temporary activation, thereby regulating venous outflow.

Volume-dependent intracavernous hemodilution during pharmacologically induced penile erections

The change in the cavernous hematocrit following induction of pharmacological erection by an intracavernous injection of papaverine hydrochloride was documented in normal controls and patients with impotence. Blood samples taken from the penile cavernosa showed a significantly lower hematocrit compared to the systemic venous blood in all normal subjects. The decrease in the cavernous hematocrit was attributable to dilution of the cavernous blood pool by the injected volume of the drug, since this was not observed in erections produced by visual sexual stimulation. It appears that a restriction of the cavernous venous outflow in response to papaverine injection causes sequestration of the diluted blood in the cavernous compartment. The degree of cavernous hemodilution was found to aid in the differential diagnosis and was especially valuable in differentiating patients with arteriogenic impotence from those with venous leakage.